This invention relates to the stabilization of organic material normally tending to deteriorate. In particular, the invention relates to the protection of synthetic polymers against the harmful degradative effects, such as discoloration and embrittlement, caused by exposure to light, especially ultraviolet light.
It is known that actinic radiation, particularly in the near ultraviolet region, has a deleterious effect on both the appearance and properties of organic polymers. For example, normally colorless or light colored polyesters yellow on exposure to sunlight as do such cellulosics as cellulose acetate. Polystyrene discolors and cracks, with accompanying loss of its desirable physical properties when exposed to actinic light, while vinyl resins, such as polyvinyl chloride and polyvinyl acetate, spot and degrade. The rate of air oxidation of polyolefins, such as polyethylene and polypropylene, is materially accelerated by ultraviolet light.
In U.S. Pat. No. 3,120,540 there is discussed the reaction of substituted 4-piperidinol compounds with acid anhydrides having formula ##STR2## where n is 1 to 4, to yield bis(polymethyl)-4-piperidyl alkanoates. In the example of this patent the salt of 1,2,2,6,6-pentamethyl-4-piperidinol with the acid of formula is a plausible intermediate in the synthesis of the bis(hydrogen sulfate)salt of bis(1,2,2,6,6-pentamethyl-4-piperidyl)succinate. The compounds of U.S. Pat. No. 3,120,540 are taught to possess significant pharmacological activity in lowering blood pressure. We have now found that acid half esters of hindered piperidines stabilize organic substrates against the degradative effect of ultraviolet light.